1. Field of the Invention
The present invention relates to an image transfer apparatus and method for placing an image sheet and an image-receiving sheet one above the other to transfer an image on the image sheet to the image-receiving sheet.
2. Description of the Related Art
When a number of sheets are printed by fabricating printing plates formed of plate making material, such as PS plates, from a color original, a color proof is first prepared for a color proof operation.
Known photosensitive materials include those used in a silver-salt photographic process or electro-photographic process, as well as photopolymers. A color proof is produced by exposing an image to a photosensitive material for printing, then developing the printed image, and finally transferring the developed image to an image-receiving sheet.
Four types of photosensitive materials are employed to prepare image sheets having respective color images of black, cyan, magenta and yellow. Then, these images are successively transferred to the same image-receiving sheet so as to produce a multi-color image.
A transfer apparatus for successively transferring images from four image sheets to an image receiving sheet has been proposed in Japanese Patent Application No. 1-193632. With such an apparatus, each of the image sheets and the image-receiving sheet are placed on a guide plate in proper alignment. Subsequently, the image sheet and the image-receiving sheet are transported in one direction, passed through a transfer station of the transfer apparatus, and then transported in an opposite direction so as to be passed through the transfer station, again thereby allowing the image on the image sheet to be transferred to the image-receiving sheet.
With the above-described transfer apparatus, an operator must manually conduct the operations of covering the guide plate with the image sheet and the image-receiving sheet placed thereon with a cover sheet before transfer, and exfoliating the cover sheet after transfer. That is, leading ends of the cover sheet and the guide plate are secured to each other, and the operator pulls the cover sheet from its trailing-end side over to the transfer station. In this state, after the image sheet and the image-receiving sheet are positioned on the guide plate, the cover sheet is brought down from over the transfer station to cover them. In addition, after transfer, the operator exfoliates the cover sheet and pulls it to over the transfer station. In this state the image sheet is removed from a support plate, and an ensuing image sheet is positioned on the image-receiving sheet placed on the guide plate.
Thus, since the operation of covering the image sheet and the image-receiving sheet with the cover sheet and the operation of exfoliating the cover sheet are manually conducted, the cover sheet is liable to be damaged and stained, and the operation becomes complicated. In addition, since the positioning of the image sheet and the image-receiving sheet is effected with the cover sheet tucked up over the transfer station, the cover sheet can slip off the transfer station during the positioning operation, thereby hampering the positioning operation.
In addition, while a transporting sheet assembly is being transported in the opposite direction, the cover sheet can curl up and wrapped around a roller of the transfer station, thereby causing damage to the cover sheet to be damaged such as by.